Signalling systems for pulse telecommunication system



SIGNALLING SYSTEMS FOR PULSE TELECOMMUNICATION SYSTEM Filed Marqn 18, 1952 J. OSWALD May 28, 1957 3 Sheets-Sheetl 1 My 28;'1957 J. oswALD 2,794,072

SIGNALLING SYSTEMS FOR PULSE TELEcoMMUNIcATIoN SYSTEM Filed arch 18, 1952 3 She`ets-Sheet 2 5:9. 2 mvemrnn:

May 28, 1957 J. oswALD 2,794,072

SIGNALLING SYSTEMS FOR PULSE TELECOMMUNICATION SYSTEM Filed March 18, 1952 l 3 Sheets-Sheet 3 INVE NTORI TAcq us5 Os w/Lo United States Patent O SIGNALLING SYSTEMS FUR PULSE TELE- COMMUNICATON SYSTEM Jacques-Oswald,` Paris, Francefassignorto Compagnie Industrielle `des Telephones, Paris, France, a corporation of France Application March-18,I 1952, Serial/No. 277,235 Claims priority, application. France April17, 1951 s claims. (ci. 17a- 15) ,The present 'invention relatesto'signalling systems for pulse teleconnnunication systems 'with' one or more channels.

ln the multi-channel or multiplex systems, as is well known, there corresponds to each channel an impulse having Ia predetermined repetition period the voice current modulation being translated by a variation of the amplitude, orthe duration or of the timeof appearance ofthe pulse.

In the majority of the well-known systems, the signal-l ling is carried out` by the transmission ofl -a panticular voice frequency which modulates the impulse under the same conditions asthe voice currentsgor again by partials or total suppression of the channel impulse.

The present'invention makes it possible toovercome the difficulties encountered in making'fthe callI by` voice fre-1 quency, particularly# the untimely releases or lack of' sensitivity of thefringers.

The object ofthe 'present invention isfa method of signalling for a pulsel transmission system, characterised in this,- that the transmission of a signallingf'current on a` transf mission channel-employing a series ofy impulses of. frequencyfF, causes the'suppressionof oneimpulse in two in the series ofsaid channel impulses, so as to transmit the frequency F/Zand its odd multiplies-'during thel period of transmission of the signalcurrents.r l

The spectrum of a series of periodic impulses of frequency Fy comprises the. frequency lines F, 2F, 3F nF, etc. the amplitude of which lines decreases very slowly'with. the-degree, when the'duration of the pulses arr etc. The appearance of any one of the odd multiple frequencies of F/2 characterises the signalling, so that in the receiving device, the selection of any one of these frequencies, for example 3F/ 2, releases, after amplification and detection, the call receiving relay.

The characteristics of the invention will appear from the following description of an example of the application of the invention to multiplex systems, with reference to the attached drawings, in which:

Fig. l shows the circuit diagram of a device utilising the method of signalling in accordance with the invention;

Fig. 2 shows a graph of the transformation of the 2,794,012 Patented May 28., 15957 ICC channel currents in the members of the transmitting device of Fig. 1;'

Fig. 3 shows anotherform of the member eliminating one impulse in two in the series of channel impulses.

In the diagram of Fig. l, 1 represents' a sinusoidal oscillator -at the frequency F/2, for example 4 kcs. if the repetition frequency F be fixed at 8 kcs. 2 is a limiter comprising, for example, a valve, and transforming the sinusoidal oscillation offrequency F/ 2 intoa rectangular wave of -the same frequency. 3fis a devicev for deviation in relation to time comprising for'example a network with time constant or a retardation line having one end shortcircuited and transforming the. rectangular wave into short, yalternately positive and negative impulses.

The interval between two successive impulses of opposite polarity is T= microseconds, in the example chosen. Fig. 2 showsthe transformation of the sinusoidal oscillation in the members 1, 2 and 3 (series 2.1, 2.2 and 2.3).

4 is' a retardation line which staggers in time the impulses of double polarity, the tappings 5 making it possible to take off the currents corresponding to the various channels through a resistance. applied througha transformer 6 tothe rectifier bridge 7 of which the connections depend on the ringing relay 8-.

In the absenceof signalling current, the relay 8 is at the normal position, Iand the connections ensured by its rest contacts arek such that the positive pulses reach a channely modulator 9" without alteration', and that the negative pulses are rectified before being applied to the modulator.- The modulating impulsesare therefore in thisy case in conformity with tlie seriesV 2.4 shown in Fig. 2. The modulator 9 may beany member whatsoever supplying at its output terminals 10 impulses which are modulated in amplitude, yduration or position, when it receives on the one hand the impulses coming'from the rectifier bridge 7 andon the other hand the voice currents coming from a differential transformer 11 associated with the two-wire line 12 `andterminated byV a balancing network 13. The terminals 10 areconnected to meansy for communicating with the receiver portion of the associated station by means of an unillustrated mixing apparatus for the impulses coming from the diierent channels.

When a signalling current is transmitted at 12 the relay 8 energised by the currents rectified -by ythe rectifier 14 pulls up and its make contacts modify the connections ofy two of the rectiers'of the bridge 7. The connections ensured are such that the impulses of positive polarity are not disturbed, while the negative impulses are eliminated, two of the rectiers playing the part of short ':ircL-lit.'` In theserconditionswe find on the output termina1s10 of themodul-ator 9 kpositive impulses at intervals of 2T, (250- microsecondsA inthe example chosen) inv accordance with the series 2.5 of Fig. 2.

It is noteworthy that the blocking and rectifying operations can be carried out in separate members, the connections of the blocking member alone being dependent on the position of the call transmitting relay. Such an arrangement is shown in Fig. 3, where it will be seen that the armature of the call-transmission relay 8 closes in its operative position, on the terminals of the secondary winding of the transformer 6, a shunt comprising rectifiers 25, which place the impulses of the `direction to be elirninated in short-circuit.

The call-transmitting relay may, of course, be replaced by a static blocking device controlled by the ringing current.

In the receiving device, the duration-modulated or amplitude-modulated channel pulses coming from the corresponding transmitting station and received at the terminals 25, are applied to the input terminals 26 of diien The channel impulse is ent channel selectors 15, that also receive on its terminals 27 a selection pulse characteristic of the channel concerned. The selector may be of any kind, for example, a device with valves or a blocking device with rectifier cells. The channel pulse selected at 28, is `applied to a lowpass lter 16 and to a band-filter 17 arranged in parallel.

When the voice currents modulate the channel impulses of frequency F (here 8 kcs.) the filter 16 separates the telephone modulation which is applied to the grid of a valve 18 by means of a transformer 19. After amplication the voice currents pass into a low-pass iilter 20 of which the cut-oli frequency is 4 kcs., and are sent on the differential 11 of the line 12. The band lter 17 tuned to the frequency 3F/2 (here 12 kes.) only receives very weak currents which only come from the components at 4 kcs. of the voice currents, transposed to l2 kcs. in the upper band of modulation associated with the frequency F.

Thus the band lter 21 tuned to SF/ 2 l2 kes.) is traversed by fan extremely weak current which cannot, after passing into a rectifier 22 energise =a call receiving relay 23.

When a signalling current is emitted by a subscriber, the frequency of repetition of the impuses selected at 15 is F/ 2. The filter 16 slightly attenuates the frequency .F 2, the filtering effect being completed by the filter 2G. On the other hand the iilter 17 passes the frequency 3F/2 (l2 kcs.) which is amplified by the valve 18 before passing into fthe band-pass filter 21 and energising, after detection, the relay 23 which controls the closing on the line 12 of a local source 24 and the opening of the circuit of ringing relay 8.

According to another embodiment, the call-transmitting device remaining the same, the filter 17 of the receiving system is eliminated and the iilter 16 is established in order to pass the frequency F/ 2 (4 kcs.). The currents of frequency F/ 2 energise the relay 23 after passing in the filter 21 tuned to 4 kes. The call is thus made at a frequency F/ 2 of the voice band. The device, however, has a great advantage over that which consists in modulating the transmission pulses art 4 kcs. In effect, the amplitude of the component F/ 2 (4 kes.) is incomparably higher (in a ratio of several nepers) when one impulse in two is suppressed than when the impulse of frequency F is modulated by a frequency F/2, because in the latter case the rate of modulation is of necessity very low in order to prevent distortions andcross-talk.

The method and devices described above may also be applied in the case of a single-channel link.

What is claimed. is:

l. In a transmitting station of a multi-channel installation for voice transmission by electrical impulse signals in which the impulse signals for each voice transmission in each channel are emitted with a repetition frequency F, and in which the calling signals for each channel are obtained by suppressing every other impulse signal, in combination, an impulse generator for providing a series of alternately positive and negative electrical impulses at a repetition frequency F, said impulse genera- 4 tor having output terminals; a calling relay having a plurality of fixed contacts and a plurality of movable contacts, said movable contacts being movable between at least two dilerent positions in each of which said movable contacts engage diierent ones of said fixed contacts; and a plurality of rectifiers connected in circuit between said output terminals of said impulse generator and said contacts of said calling relay in such manner that, in one position of said movable contacts, said rectiers suppress all of the impulses of one polarity emitted from said impulse generator and in the other position of said movable contacts of said calling relay, said rectiers invert all of the impulses of said one polarity.

2. In a transmitting station of a multi-channel installation for voice transmission by electrical impulse signals in which the impulse signals for each voice transmission in each channel are emitted with a repetition frequency F, and in which the calling signals for each channel are obtained by suppressing every other impulse signal, in combination, an impulse generator for providing a series of alternately positive and negative electrical impulses at a repetition frequency F, said impulse generator having output terminals; a calling relay having a plurality of xed contacts and a plurality of movable contacts, said movable contacts being movable between at least two different positions in each of which said movable contacts engage dierent ones of said lixed contacts; and a plurality of rectiters connected in circuit between said output terminals of said impulse generator and said contacts of said calling relay in such manner that, in one position of said movable contacts, said rectiers are connected in a bridge circuit and in the other position of said movable contacts of said calling relay, at least two of said plurality of rectiiers are connected in series across the output terminals of said impulse generator.

3. In a transmitting station of a multi-channel installation for voice transmission by electrical impulse signals in which the impulse signals for each voice transmission in each channel are emitted with a repetition frequency F, and in which the calling signals for each channel are obtained by suppressing every other impulse signal, in combination, an impulse generator for providing a series of alternately positive and negative electrical impulses at a repetition frequency F, said impulse generator having output terminals; a calling relay having at least one contact; a plurality of irst rectifiers connected as a bridge circuit to said output terminals of said impulse generator; and a second rectilier connected between said output terminals of said impulse generator and said contact of said calling relay so that said second rectier may be connected across said output terminals whenever desired.

2,539,497 Treadwell Jan. 30, 1951 Hurault Oct. 7, 1952 

